US3463732A - Polarizable ferroelectric ceramic compositions - Google Patents

Description

3,463,732 POLARIZABLE FERROELECTRIC CERAMIC COMPOSITIONS l-Iisao llanno, Aichi Prefecture, and Tsutomu Tsunooka, Kuriya, Japan, assignors to NGK Spark Plug Co., Ltd., Nagoya, Japan No Drawing. Filed July 5, 1967, Scr. No. 651,112 Claims priority, application Japan, Au". 26, 1966, 41/ 55,798 Int. Cl. C(Mb 35/00, 35/46; H01v 7/02 US. Cl. 25262.9 26 Claims ABSTRACT OF THE DISCLOSURE A novel and useful polarizable ferroclectric ceramic composition suitable for use in piezoelectric and electrostrictive ceramic articles and consisting essentially of a series of solid solutions expressed by the formula,

Pb(W hla g) wherein Ma represents at least one clement selected from the group consisting of Ni and Zn, or another series of solid solutions expressed by taining Mn at a rate corresponding to up to 5.0 Weight percent of MnO in the aggregate.

This invention relates broadly to compositions of mat ter and articles of manufacture fabricated therefrom.

More particularly, the invention pertains to novel ferroelectric ceramics susceptible of electrostatic polarization and exhibiting, when polarized, electromechanical transducing properties similar to the well-known piezoelectric effect. As a result of these properties, materials, of the type to which the present invention pertains have come to be known and may hereinafter be referred to as piezoelectric ceramics. \Vhile the principal product contemplated by the invention is the matured and polarized ceramic, as well as articles fabricated therefrom, it is to be understood that it also encompasses as intermediates the unreacted physical mixture of raw materials and the heat reaction product of such mixtures. Accordingly, the term ceramic compositions will be used herein to encompass and designate generically the compositions of matter at all stages from the unreacted physical mixtures to the matured and polarized ceramic which is the ultimate product.

Polarizable ferroelectric ceramic compositions for use in piezoelectric and electrostrictive elements have a perovskite structure expressed by the formula ABO wherein A represents a bivalent metal ion and B represents a four valent metal ion. But, all of the compounds having the perovskite structure do not always exhibit piezoelectric and electrostrictive properties. Some of them such as barium titanate, BaTiO singly exhibit piezoelectric and electrostrictive properties, another of them such as lead titanate zirconate, PbTiO PbZrO do not individually exhibit, as lead titanate and lead zirconate, piezoelectric and electrostrictive properties, but as a solid solution of at least two. for example, two of them exhibit piezoelectric 3,463,732 :ntecl Aug. 26, 1969 and electrostrictive properties, whilst ABO structure wherein B representing four valent ion consists of two ions having different ionic valency such as Mifg-MZE or Mfg-M2,;

wherein M M and M show divalent, six valent and five valent metal ions, respectively, shows as singly or as complex solid solution with another A130 structure piezoelectric and electrostrictive properties.

The inventors have found out that Pb(W l\ia )O having the pervoskite structure wherein W having M and Ma having l\i and representing at least one element selected from the group consisting of Ni and Zn are located at the position B of A130 does not singly exhibit the piezoelectric and electrostrictive properties in a manner similar to PbTiO but solid solutions expressed by the formula wherein x=0.2 to 0.7, solid solutions expressed by the formula (VI/'2 A131,?) wherein Mb represents at least one element selected from the group consisting of Zr and Sn, and x=0.02 to 0.7,

y=0.l to 0.8, $20 to 0.75 and x+ *+z=l.0, and solid solutions expressed by said formulas wherein from zero to 20 atoms percent of Pb is replaced by at least one alkaline earth element selected from the group consisting of Ba, Ca and Sr and further containing Mn at a rate corresponding to up to 5.0 weight percent of MnO in the aggregate conspicuously improve the mechanical quality factor Qm.

The principal object of the invention is to provide a novel and useful polarizable ferroelectric ceramic composition suitable for use in electromechanical transducer elements.

Another object of the invention is to provide a polarizable ferroelectric ceramic composition having a very high mechanical quality factor.

The invention will be explained with reference to the following examples.

EXAMPLE 1 PbO, W03, Z110, Tloz, Zl'Og, S1102, BHCOQ, CaCO and SrCO; were admixed and ground such that ceramics having compositions shown in the following Tables 1 and 2 were obtained. Then the product thus obtained was molded and calcined at a temperature of 700 to 1,000 C. and then ground again and sintered in PbO atmosphere at a temperature of 1,100 to 1,400 C. to obtain a disk having a diameter of about 20 mm. and 0.8 mm. in thickness. This disk thus obtained was electroded at each main surface with a silver electrode and polarized for one hour by applying a direct current electric field of 3.2 kv. (4O kv./cm.) at a temperature of 80 C. This disk thus treated was stored in the air at room temperature for one week and then the electromechanical coupling coefficient kp. and dielectric constant e of the disk were measured. The results thus obtained were shown in the following Tables 1 and 2.

TABLE 1 Electromechanical coupling coetfi- Dielectric cient, eonstant, kp. e

Composition (molar ratio) PDQVt-g-Nlg-QO; lbTiO; PbY-rO;

PlJSllO3 Sample No:

place of Pb(Wi/2-Nl 0 TABLE 2 D ielectric. constant,

Composition hp. 2

or xPb(W -Ma )O yPbTiO zPbMbO wherein up to 20 atom percent of Pb is replaced by at least one alkaline earth element selected from the group consisting of Ba, Ca and Sr showed at least 0.1 of electromecharical coupling coefiicient kp. and at least 300 of dielectric constant e and were suitable for use in practice as piezoelectric and electrostrictive ceramics. The range of x=0.09 to 0.45, y::0.25 to 0.65, z=0.25 to 0.6 and .r+y+z=l.0 exhibiting more than 0.3 of electromechan- EXAMPLE 2 PbO, W0 NiO, TiO- and ZrO were admixed such that the basic composition expressed by the formula, O-3Pb(V1 2'Ni1 2)O30.5PbTiO -0.2PbZrO \Vas Obtained. The composition thus obtained was further added with MnO and ground. The product thus obtained was molded and calcined at a temperature of 700 to 900 C. and then ground again and molded and subsequently sintered in PbO atmosphere at a temperature of 1,000 to 1,300 C. to obtain a disk having a diameter of about 20 mm. and 0.8 mm. in thickness. This disk was electroded at each main surface with a silver electrode and then polarized by applying direct current electric field of 3.2 kv. (4O kv./cm.) at a temperature of 80 C. for one hour. This disk was then stored in the air at room temperature for one week and electromechanical coupling ooefiicient kp., dielectric constant e and mechanical quality factor Qm of the disk were measured. The results As can be seen from the above Tables 4 and 5,

wherein Ma represents at least one element selected from coefficient kp. which can practicably be used as piezoelectric and electrostrictive ceramics and of remarkably improving mechanical quality factor Qm. Particularly, the range of x=0.05 to 0.6, y=0.l to 0.8, z= to 0.6 and x+y+z=l.0 is preferable, because such range makes it possible to improve the mechanical quality factor Qm twice as large as that without adding MnO Manganese may be added in the form of metals, oxides or other compounds. Manganese may be added at a ratio corresponding to front 0 to 5.0 weight percent of MnO in the aggregate. In this case it is preferable to increase the amount of lead such that lead becomes in balance with manganese added.

Pb(W Ma )O PbTiO and PbMbO each constituting the basic composition according to the invention have perovskite structure expressed by the formula, A80 respectively, and do not individually exhibit piezoelectric and electrostrictive properties, but exhibit, when formed into complex solid solutions expressed by the formulas,

wherein x=0.02 to 0.7, y=0.1 to 0.8, 2 0 to 0.75 and x+y z=1.0, piezoelectric and electrostrictive properties.

When a part of Pb in the above composition of IPb(W1 2 Ma1 2)O Or xPb- (W -Ma )O -yPbTiO zPbMbO is substituted with at least one alkaline earth element selected from the group consisting of Ba, Ca and Sr, the rate of the substitution is to be less than 20 atom percent, because a substitution in excess of 20 atom percent causes remarkable deterioration of piezoelectric properties of products.

The ceramic composition according to the invention, when expressed by the above mentioned formulas, exhibits the highest piezoelectric and electrostrictive properties.

But it is difficult in practice to obtain the atomic ratio as strictly defined by the above mentioned formulas even if sintering treatment is effected in specially adjusted atmosphere or the amount of the ingredients to be added is increased beforehand in order to compensate for vaporization of the ingredients during sintering of the ceramic composition. Some deviation from the above mentioned atomic ratio is allowable since the ceramic com position according to the invention is not substantially influenced by such deviation.

What we claim is:

1. A polarizable ferroelectric ceramic composition consisting essentially of a compound expressed by the form- 2. A polarizable ferroelectric ceramic composition consisting essentially of a compound expressed by the formula, .rPb(W -Mai )O yPbTiO -zPbMbO wherein Ma represents at least one element selected from the group consisting of Ni and Zn, Mb represents at least one element selected from the group consisting of Zr and Sn, and 2. 0.02 to 0.7, y=0.1 to 0.8, 2:0 to 0.75 and x+y+z=1.0.

3. A polarizable ferroelectric ceramic composition as claimed in claim 2 wherein up to atom percent of Pb is replaced by at least one alkaline earth element selected from the group consisting of Ba, Ca and Sr.

4. A polarizable ferroelectric ceramic composition consisting essentially of a compound expressed by the formula, -hl'ln Mb represents at least one element scl-..cted f om the group consisting of Zr and Sn, and x==0.02 to 0.7, 1 0.1 to 0.8, 2:0 to 0.75 and x+y+Fl.0.

5. A polarizable ferroelectric ceramic composition as claimed in claim 4 wherein up to 20 atom percent of Pb is replaced by at least one alkaline earth element selected from the group consisting of Ba, Ca and Sr.

Ma represents at least one element selected from the group consisting of Ni and Zn, Mb represents at least one element selected from the group consisting of Zr and Sn, and x=0.02 to 0.7, 3 :01 to 0.8, 2 0 to 0.75 and x-l-y+z=l.0, said composition including, as a substituent for an equivalent amount of lead therein, from zero to 20 atom percent, in the aggregate, of at least one alkaline earth element selected from the group consisting of Ba, Ca and Sr, and further containing manganese in an amount corresponding to from zero to 5.0 weight pet'- cent of MnO in the aggregate.

6. A polarizable ferroelectric ceramic composition consisting essentially of a compound expressed by the formula, xPb(W -Zn )O yPbTiO -:PbMbO wherein Mb represents at least one element selected from the group consisting of Zr and Sn, and x 002 to 0.7, y=0.l to 0.8, 1:0 to 0.75 and x+y+z=1.0.

7. A polarizable ferroelectric ceramic composition as claimed in claim 6 wherein up to 20 atom percent of Pb is replaced by at least one alkaline earth element selected from the group consisting of Ba, Ca and Sr.

8. A polarizable ferroelectric ceramic composition consisting essentially of a compound expressed by the formula, xPb(W 'ri )O (1x)PbTiO wherein 2. 0.2 to 0.7.

9. A polarizable ferroelectric ceramic composition as claimed in claim 8 wherein up to 20 atom percent of Pb is replaced by at least one alkaline earth element selected from the group consisting of Ba, Ca and Sr.

10. A polarizable ferroclectric ceramic composition consisting essentially of a compound expressed by the formula, .rPb(W -Zn )O 'PbTiO -zPbMbO wherein Mb represents at least one element selected from the group consisting of Zr and Sn, and x=0.09 to 0.45, y'=0.25 to 0.65, z=0.25 to 0.6 and x+y+z=1.0.

11. A polarizable ferroelectric ceramic composition as claimed in claim 10 wherein up to 20 atom percent of Pb is replaced by at least one alkaline earth element selected from the group consisting of Ba, Ca and Sr.

12. A. polarizable ferroelectric ceramic composition consisting essentially of a compound expressed by the formula, xPb(W -Ni )O yPbTiO -zPbMbO wherein Mb represents at least one element selected from the group consisting of Zr and Sn, and x=0.09 to 0.45, 0.25 to 0.65, z=0.25 to 0.6 and x+y+z=1.0.

13. A polarizable ferroelectric ceramic composition as claimed in claim 12 wherein up to 20 atom percent of Pb is replaced by at least one alkaline earth element selected from the group consisting of Ba, Ca and Sr.

14. A polarizable ferroelectric ceramic composition consisting essentially of a compound expressed by the form- 15. A polarizable ferroelectric ceramic composition consisting essentially of a compound expressed by the formula,

form ula,

wherein Ma represents at least one element selected from the group consisting of Ni and Zn, Mb represents at least one element selected from the group consisting of Zr and Sn, and x=0.02 to 0.7, y=0.1 to 0.8, 2:0 to 0.75 and x+y+z=1.0, and further containing manganese in an amount corresponding to up to 5.0 weight percent of MnO in the aggregate.

17. A polarizable ferroelectric ceramic composition as claimed in claim 16 wherein up to Z atom percent of Pb is replaced by at least one alkaline earth element selected from the group consisting of Ba, Ca and Sr.

18. A polarizable ferroelectric ceramic composition consisting essentially of a compound expressed by the formula,

wherein Mb represents at least one element selected front the group consisting of Zr and Sn, and x=0.05 to 0.6, y==0.1 to 0.8, z=0 to 0.6 and x+y+z=l.0, and further containing manganese in an amount corresponding to from 0.05 to 5.0 weight percent of MnO in the aggregate.

19. A polarizable ferroelectric ceramic composition as claimed in claim 18 wherein up to 20 atom percent of Pb is replaced by at least one alkaline earth element selected from the group consisting of Ba, Ca and Sr.

20. A polarizable ferroelectric ceramic composition consisting essentially of a compound expressed by the formula,

xPb(\V 2111 2) wherein Mb represents at least one element selected from the group consisting of Zr and Sn, and x=0.05 to 0.6, :01 to 0.8, z=0 to 0.6 and x+y+z=1.0, and further containing manganese in an amount corresponding to from 0.05 to 5.0 weight percent of MnO in the aggregate.

21. A-polarizable ferroelectric ceramic composition as claimed in claim 20 wherein up to 20 atom percent of Pb is replaced by at least one alkaline earth element selected from the group consisting of Ba, Ca and Sr.

22. A polarizable ferroelectric ceramic composition consisting essentially of a compound expressed by the formula,

wherein Mb represents at least one element selected from the group consisting of Zr and Sn, and .t'=0.05 to 0.6, y=0.1 to 0.8, z=0 to 0.6 and x-i-y{-z=l.0, and further containing manganese in an amount corresponding to about 0.5 weight percent of MnO in the aggregate.

23. A polarizable fcrroelectric ceramic composition as claimed in claim 22 wherein up to 20 atom percent of Pb is replaced by at least one alkaline earth element selected from the group consisting of Ba, Ca and Sr.

24. A polarizable ferroelectric ceramic composition consisting essentially of a compound expressed by the formula,

xPb(W1/2Zn1 2)O3)'PbTiO --ZPbh bO3 wherein Mb represents at least one element selected from the group consisting of Zr and Sn, and x=0.05 to 0.6, y=0.l to 0.8, 1 0 to 0.6 and x+)'-i2=l.0, and further containing manganese in an amount corresponding to about 0.5 weight percent of MnO in the aggregate.

25. A polarizable ferroelectric ceramic composition consisting essentially of a compound expressed by the formula,

References Cited UNITED STATES PATENTS 3,372,121 3/1968 Banno 25262.9

TOBIAS E. LEVGW, Primary Examiner I. COOPER, Assistant Examiner US. Cl. X.R. 10639 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,463 ,732 August 26 1969 Hisao Banno et a1.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading to the printed specification, line 9,

"4l/S5,798" should read 4l/74,0S4 Column 2, line 4,

2+ 5 M h 1d d 5 cu rea M 5/3 Columns 3 and 4, TABLE 1, fourth column, line 32 thereof "0.1" should read 0.4 Columns 5 and 6, TABLE 4, eithth column,]

16 thereof, "850" should read 857 Signed and sealed this 10th day of November 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer